This Invention relates to covers used in nautical applications to cover openings in the hulls of ships including submarines and other devices used in water environments especially in oceans, seas and large fresh water bodies such as the Great Lakes.
These hull openings, called sea chests and side thrust covers, usually take form of cavities of various shapes. To prevent water in the sea chests from entering the interior of a ship, these sea chests are sealed to the interior of the hull and are frequently an integral part of the hull.
Within the sea chest can be found valves to regulate intake or exhaust of water between the ship's interior and the ocean or whatever body of water surrounds the ship, for the purposes stated in my U.S. Pat. No. 5,692,451, which disclosure is incorporated herein by reference.
To prevent debris, floating material, shells and waste of any kind from entering a chest, a cover shaped to the contour of the ship's hull at the location of the chest, is applied to the chest opening. These covers are frequently made of cast iron or steel. Further, these covers are designed to allow passage of water between the chest and the ocean in response to pressure differences. This free passage is guaranteed by providing holes in the covers. These are drilled or are formed when the covers are fabricated from rods welded to form an array of spaced horizontal and vertical rods. Other manufacturing techniques exist. The holes or the openings in the grid act as filters to keep out debris and to allow free movement of water through the cover.
A major difficulty with the covers is the growth of algae, barnacle, etc. on the surface of both cast iron and steel covers. Such growth in time diminishes flow of water into and out of sea chests putting pressure on the pumps used to move the water, and changing the rate at which the water is moving.
Another difficulty arises from the oxidizing of the covers, especially of those formed from cast iron. Both the cast iron and the steel covers suffer from deposits of salts due to the electrolytic reactions stemming from the dissimilar metals of hull and covers in a bath of essentially dissociated ionic salts. To overcome these shortcomings, the covers are painted with anti fouling paints. This remedy is at best moderately successful and expensive since the procedure requires the ship to be in dry dock. The procedure is cyclical. Any breaks in the thin protective coat of paint become a starting point for erosion.
A third problem arises from pitting of the metal surface of the covers and from the inherent crystalline formation especially of the surface of the cover. The erosion caused by scouring effect of a ship's movement in the water and the release of dissolved air bubbles in bursts of high speed micro bubbles, in time flake off paint and pit the metal of the covers. This pitting enhances the growth of barnacles, algae and other forms of marine life by supplying a foothold or anchor to the metal covers. From this point on, the rate of erosion increases due to the waste given off by the marine organisms.
Finally, in journeys in cold waters, ice crystals grow on the metal covers because the covers are excellent heat conductors and release heat energy to the cold water and at equilibrium ice crystals form because the pitted surface of the covers act like nuclei for the attaching of ice crystals. Heating techniques to remove the ice, though effective, proved to be prohibitively expensive. The remedy in all such cases is periodic removal of the ice, a task for divers, or again putting the ship in dry dock, either way an operation both costly and time consuming.
The invention disclosed in U.S. Pat. No. 5,692,451 proposed a one-time remedy for these problems at sizeable savings in time and money. The problems, as pointed out previously, stem from the following facts:                1. Debris that must be kept out of the sea chests impinging on the sea chest cover and damaging the thin coating.        2. The rough surface of cast iron and of steel exacerbate the problem by pitting due to turbulence as water passes over or through covers causing destructive gas bubble pressures.        3. Different metals in an electrolytic solution cause deposition of ionic salts.        4. Diminishing efficiency of covers as marine growth changes the effective shape of waterways through the covers        5. Increase in turbulence and noise from changes in cover configuration and in growth of marine life attached to the cover.        6. Deposits of ice when ship operates in cold waters.The remedies flow from the invention design and are not simply applied to some base structure. The invention explicitly calls for the construction of sea chest covers from viscoelastic plastic to replace cast iron, steel, fiberglass or other metals or alloys. Among the effective plastics are the ones in the class of polyurethanes, high density and ultra-high density polyethylenes and copolymers thereof. These may be compression molded. The plastics mentioned and others of like characteristics exhibit the following properties:        1. Ability to be fabricated with tough, smooth high-density skin. The advantages gained are the following: algae and other marine life forms requiring an anchor for food to be transported to them, cannot form these anchors on a surface essentially free of pit marks.        2. All edges on the covers as depicted in this invention are formed with a radius rather than with square sharp edges to reduce turbulence.        3. Compared to cast iron and steel, the viscoelastic plastics of the covers cushion vibration and reduce noise generated both from the water moving through the grid of the cover and from hull vibrations.        4. The need for anti fouling paint to protect the covers no longer exists.        5. Hard ice will not form on the covers since no sites to act as nuclei exist on the smooth plastic surface.        